Women in a clinical trial who became pregnant after vaccination with a human papillomavirus (HPV) vaccine did not have an increased risk of miscarriage compared with women who were not exposed to the vaccine, according to a new analysis of additional data from a clinical trial conducted in Costa Rica.

The trial evaluated the efficacy of a vaccine manufactured by GlaxoSmithKline that is now sold as Cervarix. This vaccine is known as a bivalent HPV vaccine because it protects against infection with two HPV types, 16 and 18. Together, these types cause most (about 70 percent) cervical cancers and some other anogenital and head and neck cancers.

The Food and Drug Administration has approved three vaccines to protect against infection with types of HPV that can cause cancer. Because the vaccines may be given to women of reproductive age, any effect of HPV vaccines on the ability to carry a pregnancy to term would be a concern.

In the new analysis, the researchers assessed the risk of miscarriage among close to 10,000 young adult women who were part of the NCI Costa Rica HPV Vaccine Trial and the trial’s extended follow-up. In the clinical trial, nearly 7,500 women had been randomly assigned to receive the bivalent HPV vaccine or a control vaccine (hepatitis A vaccine). The trial researchers also looked at pregnancy outcomes in a group of more than 2,800 unvaccinated women who were not part of the original randomized trial.